Intervertebral spacer device having a wave washer force restoring element

ABSTRACT

An intervertebral spacer device having a pair of opposing plates for seating against opposing vertebral bone surfaces, separated by at least one force restoring element. The preferred force restoring mechanism is a wave washer. In a first embodiment the wave washer is ring-shaped. In a second embodiment the wave washer is spiral-shaped.

CROSS-REFERENCE TO RELATED APPLICATION

This application is a continuing application of U.S. patent applicationSer. No. 09/906,117 (filed Jul. 16, 2001) entitled “IntervertebralSpacer Device Having a Wave Washer Force Restoring Element”, now U.S.Pat. No. 6,468,310, which application is hereby incorporated byreference herein in its entirety.

FIELD OF THE INVENTION

This invention relates generally to a spinal implant assembly forimplantation into the intervertebral space between adjacent vertebralbones to simultaneously provide stabilization and continued flexibilityand proper anatomical motion, and more specifically to such a devicewhich utilizes a wave washer as a force restoring element.

BACKGROUND OF THE INVENTION

The bones and connective tissue of an adult human spinal column consistsof more than 20 discrete bones coupled sequentially to one another by atri-joint complex which consists of an anterior disc and the twoposterior facet joints, the anterior discs of adjacent bones beingcushioned by cartilage spacers referred to as intervertebral discs.These more than 20 bones are anatomically categorized as being membersof one of four classifications: cervical, thoracic, lumbar, or sacral.The cervical portion of the spine, which comprises the top of the spine,up to the base of the skull, includes the first 7 vertebrae. Theintermediate 12 bones are the thoracic vertebrae, and connect to thelower spine comprising the 5 lumbar vertebrae. The base of the spine isthe sacral bones (including the coccyx). The component bones of thecervical spine are generally smaller than those of the thoracic spine,which are in turn smaller than those of the lumbar region. The sacralregion connects laterally to the pelvis. While the sacral region is anintegral part of the spine, for the purposes of fusion surgeries and forthis disclosure, the word spine shall refer only to the cervical,thoracic, and lumbar regions.

The spinal column of bones is highly complex in that it includes overtwenty bones coupled to one another, housing and protecting criticalelements of the nervous system having innumerable peripheral nerves andcirculatory bodies in close proximity. In spite of these complications,the spine is a highly flexible structure, capable of a high degree ofcurvature and twist in nearly every direction.

Genetic or developmental irregularities, trauma, chronic stress, tumors,and degenerative wear are a few of the causes which can result in spinalpathologies for which surgical intervention may be necessary. A varietyof systems have been disclosed in the art which achieve immobilizationand/or fusion of adjacent bones by implanting artificial assemblies inor on the spinal column. The region of the back which needs to beimmobilized, as well as the individual variations in anatomy, determinethe appropriate surgical protocol and implantation assembly. Withrespect to the failure of the intervertebral disc, the interbody fusioncage has generated substantial interest because it can be implantedlaparoscopically into the anterior of the spine, thus reducing operatingroom time, patient recovery time, and scarification.

Referring now to FIGS. 1 and 2, in which a side perspective view of anintervertebral body cage and an anterior perspective view of a postimplantation spinal column are shown, respectively, a more completedescription of these devices of the prior art is herein provided. Thesecages 10 generally comprise tubular metal body 12 having an externalsurface threading 14. They are inserted transverse to the axis of thespine 16, into preformed cylindrical holes at the junction of adjacentvertebral bodies (in FIG. 2 the pair of cages 10 are inserted betweenthe fifth lumbar vertebra (L5) and the top of the sacrum (S1). Two cages10 are generally inserted side by side with the external threading 14tapping into the lower surface of the vertebral bone above (L5), and theupper surface of the vertebral bone (S1) below. The cages 10 includeholes 18 through which the adjacent bones are to grow. Additionalmaterial, for example bone graft materials, may be inserted into thehollow interior 20 of the cage 10 to incite or accelerate the growth ofthe bone into the cage. End caps (not shown) are often utilized to holdthe bone graft material within the cage 10.

These cages of the prior art have enjoyed medical success in promotingfusion and grossly approximating proper disc height. It is, however,important to note that the fusion of the adjacent bones is an incompletesolution to the underlying pathology as it does not cure the ailment,but rather simply masks the pathology under a stabilizing bridge ofbone. This bone fusion limits the overall flexibility of the spinalcolumn and artificially constrains the normal motion of the patient.This constraint can cause collateral injury to the patient's spine asadditional stresses of motion, normally borne by the now-fused joint,are transferred onto the nearby facet joints and intervertebral discs.It would therefore, be a considerable advance in the art to provide animplant assembly which does not promote fusion, but, rather, whichnearly completely mimics the biomechanical action of the natural disccartilage, thereby permitting continued normal motion and stressdistribution.

It is, therefore, an object of the present invention to provide a newand novel intervertebral spacer which stabilizes the spine withoutpromoting a bone fusion across the intervertebral space.

It is further an object of the present invention to provide an implantdevice which stabilizes the spine while still permitting normal motion.

It is further an object of the present invention to provide a device forimplantation into the intervertebral space which does not promote theabnormal distribution of biomechanical stresses on the patient's spine.

Other objects of the present invention not explicitly stated will be setforth and will be more clearly understood in conjunction with thedescriptions of the preferred embodiments disclosed hereafter.

SUMMARY OF THE INVENTION

The preceding objects of the invention are achieved by the presentinvention which is a flexible intervertebral spacer device comprising apair of spaced apart base plates, arranged in a substantially parallelplanar alignment (or slightly offset relative to one another inaccordance with proper lordotic angulation) and coupled to one anotherby means of a spring mechanism. In particular, this spring mechanismprovides a strong restoring force when a compressive load is applied tothe plates, and may also permit limited rotation of the two platesrelative to one another. While there are a wide variety of embodimentscontemplated, two embodiment families are described herein asrepresentative of preferred types. Each of these embodiments includes awave washer utilized as its force restoring element.

More particularly, with respect to the base plates, which are similar inall embodiments, as the assembly is to be positioned between the facingsurfaces of adjacent vertebral bodies, and as such need to havesubstantially flat external surfaces which seat against the opposingbone surfaces. Inasmuch as these bone surfaces are often concave, it isanticipated that the opposing plates may be convex in accordance withthe average topology of the spinal anatomy. In addition, the plates areto mate with the bone surfaces in such a way as to not rotate relativethereto. (The plates rotate relative to one another, but not withrespect to the bone surfaces to which they are each in contact with.) Inorder to prevent rotation of a plate relative to the bone, the upper andlower plates may each include outwardly directed spikes which penetratethe bone surface and mechanically hold the plates in place.Alternatively, the base plates may be coupleable to other securing meansfor holding the present invention in place.

It is further anticipated that the plates may include a porous coatinginto which the bone of the vertebral body can grow. (Note that thislimited fusion of the bone to the base plate does not extend across theintervertebral space.)

Between the base plates, on the exterior of the device, there isincluded a circumferential wall which is resilient and which simplyprevents vessels and tissues from growing into the interior of thedevice. This resilient wall may comprise a porous fabric or asemi-impermiable elastomeric material, and serves a similar purpose tothe naturally occurring annulus material which surrounds the cartilageof the intervertebral disc, which the present invention is designed toreplace when conditions warrant. Suitable tissue compatible materialsmeeting the simple mechanical requirements of flexibility and durabilityare prevalent in a number of medical fields including cardiovascularmedicine, wherein such materials are utilized for venous and arterialwall repair, or for use with artificial valve replacements.Alternatively, suitable plastic materials are utilized in the surgicalrepair of gross damage to muscles and organs. Still further materialswhich could be utilized herein may be found in the field of orthopaedicin conjunction with ligament and tendon repair. It is anticipated thatfuture developments in this area will produce materials which arecompatible for use with this invention, the breadth of which shall notbe limited by the choice of such a material.

As introduced above, the internal structure of the present inventioncomprises a force restoring member, which provides a restoring forcewhen compressed. More particularly, it is desirable that the restoringforces be directed outward against the opposing plates, when acompressive load is applied to the plates.

In addition, in certain select embodiments, it is necessary that therestoring force providing subassembly not substantially interfere withthe rotation of the opposing plates relative to one another. In thefirst embodiment, the force restoring subassembly does not interferewith the rotation of the plates. In the second preferred embodiment, thespring subassembly substantially inhibits any rotation of the platesrelative to one another. As further mentioned above, the force restoringmember comprises at least one wave washer.

More particularly with respect to the first embodiment, in which therestoring force providing subassembly does not interfere with therotation of the plates, the restoring force providing subassemblycomprises a single wave washers. Wave washers resemble simple roundwashers which comprise a flat round ring, except that while maintaininga constant curvature of radius in the plane normally defined by thewasher, the washer rises and falls in a wave-like around itscircumference. Stated alternatively, a standard washer is a relativelyplanar ring-shaped object, confined to the x-y plane. The wave washer isring-shaped object which undulates in the z-axis around its edge. Therestoring force of a wave washer is proportional to the elasticproperties of the material. In addition, the magnitude of thecompressive load support and the restoring force provided by the wavewasher may be modified by altering the thickness of the material in itsradial extent, or in its z-axis, or, alternatively, by providing aradial slot in it. (For the purposes of this description, the top andthe bottom of a wave washer shall be defined as the planes defined bythe highest and lowest points of the circumferential undulations,respectively.)

As a compressive load is applied by a pair of plates against the top andbottom of a wave washer, the forces are directed against the arches ofthe undulating wave, and are also translated into a hoop stress whichtends to radially expand the washer in its x-y plane. This force ofdeflection against the arches, and the hoop stress in the radialdirection, are counterbalanced by the material strength of the washer.The strain of the material causes a deflection in the height of thewasher and a slight radial expansion. (It shall be understood that inthe embodiments in which the washer includes a radial slot, and in whichthe washer is constrained against radial expansion, for example by guardwalls of the corresponding base plates, the deflection of the arches isnot translated into a hoop stress, but rather into a circumferentialdeflection and closure of the slot.) Stated equivalently, a wave washerresponds to a compressive load by deflecting compressively in z-axis,and either radially or circumferentially. The restoring force which istherefore proportional to the elastic modulus. With a slot formed in thewasher, it expands and restores itself far more elastically than acontinuous ring washer.

In general, the wave washer is one of the strongest configurations for aspring, and is highly suitable for use as a restoring force providingsubassembly for use in an intervertebral spacer element which mustendure considerable cyclical loading in an active human adult. In thefirst embodiment of the present invention, the ring-shaped wave washeris secured by a series of pins which extend upwardly and outwardly fromone of the inner surfaces of one of the base plates. A compressive loadapplied to the base plates causes the corresponding compression of thewasher, which in turn causes a restoring force to be applied to the baseplates. The washer deflects appropriately under the load, only to springback into its undeflected shape upon the unloading of the spring.

It shall be understood that the securing pins, as well as the exteriorcircumferential elastomeric material place constraints on the extent towhich one base plate may rotate relative to the other. In this way thebase plates may rotate relative to one another while maintaining aconstant resilient capacity relative to the adjacent bone.

In a second embodiment of the present invention, a single modified wavewasher, which is spiral-shaped, as opposed to being ring-shaped. Moreparticularly, instead of the wave washer described in conjunction withthe first embodiment, which defines a circumference of 360 degrees (inthe solid variant) or less (the slotted variant), the wave washer of thesecond embodiment sweeps through an angle of 720 degrees or more(depending upon to specific anatomical needs). The undulations of thewasher on the z-axis may be such that the arches are aligned, ormisaligned. In the variant in which the arches are aligned, securingpins of the type introduced above (which extend upward and radiallyoutward from the interior surface of one of the base plates) may beemployed to hold the spiral wave washer in place. The alternativevariant may be secured by a simple screw which locks one of the ends ofthe washer to the base plate.

Finally, inasmuch as the human body has a tendency to produce fibroustissues in perceived voids, such as may be found within the interior ofthe present invention, and such fibrous tissues may interfere with thestable and/or predicted functioning of the device, preferred embodimentsof the present invention may be filled with a highly resilientelastomeric material. The material itself should be highly biologicallyinert, and should not substantially interfere with the restoring forcesprovided by the spring-like mechanisms therein. Suitable materials mayinclude hydrophilic monomers such as are used in contact lenses.Alternative materials include silicone jellies and synthetic collagenssuch as have been used in cosmetic applications. As with the exteriorcircumferential wall, which was described above as having a variety ofsuitable alternative materials, it is anticipated that future researchwill produce alternatives to the materials described herein, and thatthe future existence of such materials which may be used in conjunctionwith the present invention shall not limit the breadth thereof.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a side perspective view of an interbody fusion device of theprior art;

FIG. 2 is a front view of the anterior portion of the lumbo-sacralregion of a human spine, into which a pair of interbody fusion devicesof the type shown in FIG. 1 have been implanted;

FIGS. 3a and 3 b are side cross-section views of the upper and loweropposing plates of the present invention;

FIG. 4 is a side cross-section view of the opposing plates inassociation with one another, wherein an exterior skirt is included;

FIG. 5a is a perspective views of solid ring-shaped wave washer of thetype which is utilized in conjunction with an embodiment of the presentinvention, FIG. 5b is a perspective view of a slotted ring-shaped wavewasher of the type which is utilized in conjunction with a similarembodiment of the present invention, and FIGS. 5c and 5 d areperspective and top views of a spiral-shaped wave washer of the typewhich is utilized in conjunction with another embodiment of the presentinvention;

FIGS. 6a and 6 b are top and side perspective views of a securing pinassembly and screw for securing a wave washer to a base plate;

FIG. 7 is a side cross-section view of a first embodiment of the presentinvention which utilizes ring-shaped wave washer, of the type shown inFIGS. 5a and 5 b; and

FIG. 8 is a side cross-section view of another embodiment of the presentinvention which utilizes spiral-shaped wave washer, of the type shown inFIGS. 5c and 5 d;

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

While the present invention will be described more fully hereinafterwith reference to the accompanying drawings, in which particularembodiments and methods of implantation are shown, it is to beunderstood at the outset that persons skilled in the art may modify theinvention herein described while achieving the functions and results ofthis invention. Accordingly, the descriptions which follow are to beunderstood as illustrative and exemplary of specific structures, aspectsand features within the broad scope of the present invention and not aslimiting of such broad scope. Like numbers refer to similar features oflike elements throughout.

Referring now to FIGS. 3a and 3 b, side cross-section views of the topand bottom plate members 100 a 100 b of a first embodiment of thepresent invention is shown. More particularly, in this embodiment, theupper and lower plates 100 a,100 b are substantially identical. As thedevice is designed to be positioned between the facing surfaces ofadjacent vertebral bodies, the plates include substantially flat surfaceportions 102 a,102 b which seat against the opposing bone surfaces. Inaddition, the plates are to mate with the bone surfaces in such a way asto not rotate relative thereto. It is, therefore, preferred that theplates should include a porous coating 104 a,104 b into which the boneof the vertebral body can grow. (Note that this limited fusion of thebone to the base plate does not extend across the intervertebral space.)An additional threaded hole 106 a,106 b is provided in each plate suchthat the interior of the device may be readily accessed if a need shouldarise.

The plates 100 a,100 b further include a circumferential flange 108a,108 b. The flange 108 a,108 b may be offset with respect to the front110 a,110 b and rear 111 a,111 b orientation of the overall assembly.More particularly, the offset nature of the flanges 108 a,108 b isexhibited in the non-symmetric appearance of each flange as itcircumscribes the corresponding plate 100 a,100 b. By this it is meantthat the portion of the flange 108 a,108 b which corresponds to the rear111 a,111 b of the device is shorter than the portion corresponding tothe front 110 a,110 b of the device.

Referring now to FIG. 4, a partially assembled embodiment of the presentinvention is provided in a side cross-section view, wherein the upperand lower plates 100 a,100 b illustrated in FIGS. 3a and 3 b are joinedby means of a circumferential wall 120. More particularly, between thebase plates 100 a,100 b, on the exterior of the device, there isincluded a circumferential wall 120 which is resilient and which isprovided to prevents vessels and tissues from entering within theinterior of the device. It is preferred that the resilient wall 120comprise a porous fabric or a semi-impermiable elastomeric material. Thewall 120 is further designs to couple to the flanges 108 a,108 b of thecorresponding plates 100 a,100 b.

Referring now to FIG. 5a, one of the possible force restoring elementswhich may be employed with the present invention is provided in aperspective view. More particularly, the force restoring elementcomprises a ring-shaped wave washer element 130. In this embodiment, thewave washer 130 is continuous, in that it does not include a radialbreak. Stated alternatively, the ring-shaped element maintains acircumferentially complete 360 degrees. The wave washer 130 is so namedinasmuch as its circumferential conformation includes a rising andfalling undulating edge 132, which, while maintaining a constant radius,creates a periodic arches 134 and valleys 136.

The restoring force of a continuous wave washer of the type illustratedin FIG. 5a is proportional to the elastic properties of the material. Asa compressive load is applied to the continuous ring-shaped washer, theforces are directed down onto the arches 134 and up against the valleys136. A significant fraction of these forces are immediately translatedinto hoop stresses which apply stresses directed toward radiallyexpanding the washer. This hoop stress is also counterbalanced by thematerial strength of the washer.

FIG. 5b illustrates an alternative ring-shaped wave washer for use withthe present invention, which wave washer 140 is radially slotted. Thisradial slot 142 permits the compressive load which is applied to thewasher down onto the arches 144 and up against the valleys 146 to causethe ring to deflect such that the slot 142 closes. Stated equivalently,the difference between the radially slotted washer of FIG. 5b, and thecontinuous washer of FIG. 5a, is that the continuous washer 130 respondsto a compressive load by deflecting radially (with a very high stress todeflection ratio), whereas the radially slotted washer 140 deflectscircumferentially, closing the slot 142 (this is characteristic of amuch lower stress to deflection ratio).

Referring now to FIGS. 5c and 5 d, in which perspective views of a twoalternative spiral-shaped washers are provided, an alternativeembodiment category of the present invention is provided. Thespiral-shaped wave washers 150 a,150 b each comprise a spirally woundband of material (as above, a titanium alloy or stainless steel ispreferable, although other suitable surgical materials may be found tofunction adequately). As with the ring-shaped wave washers 130,140,introduced above, the spirally wound wave washers 150 a,150 b of thisembodiment style includes a series of alternating and undulating arches154 and valley 156 which extend continuously around the spiral. The wavewasher in FIG. 5c shows a washer in which the series of arches andvalleys are radially aligned. Alternatively, in FIG. 5d, the arches andvalleys are not aligned.

Referring again to FIGS. 3a and 3 b and also to FIGS. 6a and 6 b, inwhich a securing pin assembly and screw are provided, a first method ofsecuring a wave washer (either the ring-shaped washers of FIGS. 5a and 5b, or the spiral-shaped washer of FIG. 5c) to a base plate 168 isprovided. More particularly, the pin assembly 160 comprises a centralhub portion 162 which is flat and includes a threaded hole, havingsubstantially the same diameter and threading as the hole 106 a or 106 bin the corresponding base plate 100 a or 100 b. The screw 161 isdesigned to secure the pin assembly to the base plate. The pin assembly160 further includes a plurality of radially extending thin shafts 166.These shafts extend outwardly and upwardly from the base plate, aligningthemselves in the arches and valleys of the corresponding washer,thereby securing it to the base plate.

Referring now to FIGS. 3a, 3 b and 5 d, the means for securing thenon-aligned spiral-shaped wave washer is now described. At a midpoint(of a valley 156) of the spiral band of the wave washer havingnon-aligned arches 154 and valleys 156 includes a threaded hole 159which aligns with the threaded hole 106 a or 106 b in the base plate towhich it is to be secured. The screw 161 shown in FIGS. 6a and 6 bsecures the washer to the base plate through the aligned holes.

Referring now to FIG. 7, an integrated device embodying the principlesof the present invention is provided in a side cross-section view. Thebase plates 100 a,100 b are disposed in a spaced apart relationship suchthat the opposing inner surfaces are approximately parallel and facingone another. A single ring-shaped wave washer 130 or 140 is disposedbetween the plates, and retained therein by the circumferential flanges108 a,108 b. The ring-shaped wave washer 130 or 140 is furtherconstrained against rotational motion by a securing pin assembly 160,and more particularly by the radially extending thin shafts 166. Aflexible circumferential skirt 120 is provided around the entirety ofthe device, such that the tissue of the patient may not grow into, andthereby cause pain, or inhibit the functionality of the device. It shallbe understood that a very similar design would accommodate aspiral-shaped wave washer 150 a as an alternative to the ring-shapedwave washer, so long as the arches and valleys of the spiral-shaped wavewasher are radially aligned, as is shown in FIG. 5c.

Referring now to FIG. 8, an alternative integrated device embodying theprinciples of the present invention is provided in a side cross-sectionview. As with the first embodiment, the base plates 100 a,100 b aredisposed in a spaced apart relationship such that the opposing innersurfaces are approximately parallel and facing one another. In thisembodiment, a single spiral-shaped wave washer 150 b is disposed betweenthe plates, and retained therein by the circumferential flanges 108a,108 b. The spiral-shaped wave washer 150 b is further constrainedagainst undesirable translation within the assembly by means of thescrew 161 which extends through the central hole 159 of the washer 150 band the hole 106 b in the base plate 100 b. As in the first embodiment,a flexible circumferential skirt 120 is provided around the entirety ofthe device, such that the tissue of the patient may not grow into, andthereby cause pain, or inhibit the functionality of the device.

While there have been described and illustrated embodiments of anintervertebral spacer device utilizing a wave washer force restoringelement, it will be apparent to those skilled in the art that variationsand modifications are possible without deviating from the broad spiritand principle of the present invention. The present invention shall,therefore, be limited only to the full scope of the claims allowable inlight of the disclosures made herein.

What is claimed is:
 1. An intervertebral spacer device, comprising:first and second plates, the plates being disposed in a spaced apartrelationship such that one plate surface of the first plate faces oneplate surface of the second plate, the facing surfaces being innersurfaces, and alternative faces of each plate being outer surfaces; andat toast one restoring force providing element disposed between theinner surfaces of the first and second plates, and disposed such that acompressive load applied to the outer surfaces of the plates iscounteracted by the at least one restoring force providing element, theat least one restoring force providing element including at least onewave washer, the at least one wave washer having a longitudinallyundulating circumferential extent.
 2. The device as set forth in claim1, wherein the at least one wave washer comprises a ring-shaped wavewasher, the ring-shaped wave washer having a longitudinally undulatingcircumferential extent forming art uninterrupted circular hoop.
 3. Thedevice as set forth in claim 1, wherein the at least one wave washercomprises a ring-shaped wave washer, the ring-shaped wave washer havinga longitudinally undulating circumferential extent forming a circularhoop interrupted by a radial slot.
 4. The device as set forth in claim1, wherein the at least one wave washer comprises a spiral-shaped wavewasher, the spiral-shaped wave washer having a longitudinally undulatingextent tat sweeps through an angle greater than 360 degrees, such thatthe extent spirals inwardly from relatively larger-diameter outer ringportions to increasingly relatively smaller-diameter inner ringportions, the outer and inner ring pardons undulating in the samelaterally extending plane.
 5. The device as set forth in claim 1,further comprising a flexible circumferential skirt disposed about andbetween lateral perimeters of the first and second plate members,therein defining an interior volume of the device in which the at leastone wave washer is disposed.
 6. The device as set forth in claim 5,wherein the flexible circumferential skirt comprises a resilientmaterial.
 7. The device as set forth in claim 5, wherein the flexiblecircumferential skirt is porous.
 8. The device as set forth in claim 1,wherein the at least one wave washer comprises multiple wave washers. 9.The device as set forth in claim 8, wherein the multiple wave washerscomprise a plurality of concentric wave washers.
 10. The device as setforth in claim 1, wherein at least one of the first and second platesincludes a wave washer securing mechanism mounted to the inner surfacethereof.
 11. An intervertebral spacer device comprising first and secondplates, the plates being disposed in a spaced apart relationship suchthat one plate surface of the first plate faces one plate surface of thesecond plate, the facing surfaces being inner surfaces, and alternativefaces of each plate being outer surfaces; and at least one restoringforce providing element disposed between the inner surfaces of the firstand second plates, and disposed such that a compressive load applied tothe outer surfaces of the plates is counteracted by at least onespiral-shaped wave washer, the the spiral-shaped wave washer having alongitudinally undulating extent that sweeps through an angle greaterthan 360 degrees, such that the extent spirals inwardly from relativelylarger-diameter outer ring portions to increasingly relativelysmaller-diameter inner ring portions, the outer and inner ring portionsundulating in the same laterally extending plane.
 12. The device as setforth in claim 11, further comprising a flexible circumferential skirtdisposed about and between lateral perimeters of the first and secondplates, therein defining an interior volume of the device in which theat least one spiral-shaped wave washer is disposed.
 13. The device asset forth in claim 12, wherein the flexible circumferential skirtcomprises a resilient material.
 14. The device as set forth in claim 12,wherein the flexible circumferential skirt is porous.
 15. The device asset forth in claim 11, wherein at least one of the first and secondplates includes a wave washer securing mechanism mounted to the innersurface thereof.
 16. An intervertebral spacer device comprising: firstand second plates, the plates being disposed in a spaced apartrelationship such that one plate surface of the first plate faces oneplate surface of the second plate, the facing surfaces being innersurfaces, and the alternative faces of each plate being outer surfaces;and at least one ring-shaped wave washer disposed between the innersurfaces of the first and second plates, and disposed such that &compressive load applied to the outer surfaces of the plates iscounteracted by the ring-shaped wave washer, the ring-shaped wave washerhaving a longitudinally undulating circumferential extent forming anuninterrupted circular hoop.
 17. The device as set forth in claim 16,wherein the ring-shaped wave washer further includes a radial slot. 18.The device as set forth in claim 16, further comprising a flexiblecircumferential skirt disposed about and between lateral perimeters ofthe first and second plates, therein defining an interior volume of thedevice in which the at least one ring-shaped wave washer is disposed.19. The device as set forth in claim 18, wherein the flexiblecircumferential skirt comprises a resilient material.